This invention relates to temperature compensated solid state oscillators and more particularly to a temperature compensated microwave transistor cavity oscillator.
Conventional solid state oscillators employing an oscillating element disposed in a resonant cavity produce an oscillation frequency which is dependent on the physical dimensions of the oscillating element as well as the temperature characteristics of the same, and also to the bias potential applied thereto. Moreover, the oscillation frequency is also dependent on the physical dimensions of the cavity which vary with temperature. For example, with an increase in temperature the cavity size increases which therefore causes the oscillation frequency to decrease, the opposite effect occurring if the operating temperature should decrease.
Heretofore prior techniques to reduce the effects of dimensional changes of the cavity and the frequency variations caused thereby have been to construct the cavity of a material having a very small temperature coefficient of expansion, for example, Invar. However, frequency variations caused by the temperature characteristics of the oscillating element are still significant and are not compensated for by the aforedescribed cavity construction.
Another prior art method for temperature compensating an oscillator comprising a negative resistance diode (Gunn or Impatt) is disclosed in U.S. Pat. Nos. 3,623,146 and 3,665,341, both to Kaneko et. al. Here the oscillating element is disposed within a wave guide cavity having one end wall of which is a moveable plate. The moveable plate is affixed to one end of a dielectric rod having a large coefficient of linear expansion. Thus, the cavity dimension is varied over temperature in a manner to temperature compensate the oscillator.
The present invention provides a solution wherein the physical dimensions of the cavity are substantially held constant while at the same time the temperature dependent characteristics of a microwave transistor are compensated for over a wide temperature range in order to provide a very stable oscillating frequency. Thus, a solution to the problems of temperature compensating a resonant cavity oscillator is provided as will hereinafter be described.